Conventionally, a bonded-abrasive type diamond wire saw, which has diamond abrasive grains bonded to the surface of a core wire, has been proposed as an example of a superabrasive wire saw. With the diamond wire saw, a material such as a metal can be cut extremely cleanly. In addition, there is no need for a slurry having an abrasive fluid and abrasive grains blended; instead, a water-soluble or water-insoluble cutting fluid can be used. Therefore, contamination of a cutting device and its vicinity due to a sludge spattered during cutting can be prevented, and thus working environment can be improved.
In addition, the diamond wire saw can be produced to have a long length such as at least several kilometers. Therefore, a plurality of cutting processes can simultaneously be performed, and accordingly, there can be obtained a cutting rate of at least several times as high as that of a multi-wire saw type using a slurry. Such a bonded-abrasive type superabrasive wire saw is disclosed in Japanese Patent Laying-Open Nos. 8-126953 and 9-155631, International Publication No. WO 98/35784, and others.
In addition, Japanese Patent Laying-Open No. 4-351222 discloses a bonding wire winding which is wound reciprocatingly to be multi-layered such that it is unreeled smoothly during a bonding operation. For the bonding wire winding disclosed in Japanese Patent Laying-Open No. 4-351222, a bonding wire wound around a spool from one end to the other end thereof and the bonding wire further wound around the spool from the other end to the one end thereof are set to cross at an angle of at least 0.03°.
In addition, Japanese Patent Laying-Open No. 2002-18517 discloses a wire-winding device for the purpose of preventing failure in reeling the wire around a bobbin. The wire-winding device disclosed in Japanese Patent Laying-Open No. 2002-18517 is a device for winding an electric wire, a wire, and a cable around a bobbin. The wire-winding device is provided with a bobbin flange detection sensor which is capable of detecting the position of the flange. Every time the sensor detects the flange position, a moving direction of a traverser which serves to guide the wire is reversed.
In addition, Japanese Patent Laying-Open No. 2000-349120 discloses a method of winding a bonding wire for a semiconductor element for the purpose of prolonging the life of a guide, whose damage causes a flaw in the wire. In the winding method disclosed in Japanese Patent Laying-Open No. 2000-349120, a non-rotary type winding guide is used. The winding guide is formed of a hard base material coated with a diamond-like carbon film.
When a cutting process is performed using the superabrasive wire saw above, the superabrasive wire saw is provided in a reeled-up state, from which the same is unreeled toward or reeled up from a workpiece. Therefore, in order to make the superabrasive wire saw attachable to a cutting device, it is necessary to wind the same around a reel appropriate for the cutting device. FIG. 8 shows a cross section of a superabrasive wire saw wound around a reel in a conventional manner.
Referring to FIG. 8, a superabrasive wire saw 310 includes a core wire 311, and a plurality of superabrasive grains 313 bonded to a surface of core wire 311 with a bonding material 312. Unlike a loose-abrasive type, superabrasive grain 313 is provided to project from a surface of bonding material 312. Superabrasive wire saw 310 is wound around a surface of a reel 301 shaped like a cylinder reciprocatingly between the both ends of the surface to be multi-layered. Superabrasive wire saw 310 is wound with a certain pitch between the both ends of the surface of reel 301, and adjacent superabrasive wire saws 310 are in contact with each other.
When superabrasive wire saw 310 is wound around reel 301 as such, adjacent superabrasive wire saws 310 cause a friction therebetween, with the result that bonding material 312 is damaged by superabrasive grains 313. Furthermore, by an intense collision between superabrasive grains 313, superabrasive grains 313 disadvantageously fall down from the surface of core wire 311. Such problems also occur during a cutting process in which superabrasive wire saw 310 is unreeled toward or reeled up from a workpiece in a state similar to that shown in FIG. 8.